PROJECT SUMMARY Research: Gastrointestinal stromal tumors (GISTs) are among the most common mesenchymal neoplasms. Most GISTs are initiated by KIT or PDGFRA gain-of-function mutations which are therefore already found in microscopic forms of GISTs. During progression to aggressive disease, early GISTs acquire a canonical sequence of chromosomal deletions including 14q deletions that inactivate MAX, fostering cell cycle dysregulation through p16 transcriptional repression. Genomic mutations that directly inactivate p16 and other cell cycle regulators occur at subsequent stages in progression. While tyrosine kinase inhibitor (TKI) therapies for advanced GISTs result in dramatic clinical responses, secondary TKI resistance often leads to fatal disease progression, highlighting the need for novel targets defined by biologic vulnerabilities, particularly aberrations present across the entire metastatic burden in a given patient. The objective of this mentored research career development proposal is to characterize the events in GIST genomic progression that lead to incremental cell cycle dysregulation, particularly aberrations impacting p16/CDK4/RB1, with the goal of developing novel therapies for patients with advanced GIST. Leveraging GIST as a unique model amongst sarcomas to study genomic progression, my Aim 1 studies address the hypothesis that cell cycle perturbations, including targetable aberrations of the p16/CDK4/RB1 pathway, are virtually universal events in advanced GIST. The Aim 2 studies are motivated by my hypothesis that GIST responses to CDK4/6-inhibition will be maximized by combination approaches. These studies use genome-wide CRISPR screens to identify synthetic lethals with CDK4/6-inhibition in GIST. The Aim 3 studies are preclinical in vitro and in vivo validations of combination therapies that might increase GIST response to CDK4/6 inhibition. Candidate Career Goals: To expedite these translational research studies, I will foster international collaborations with experts in sarcoma genomics, biology, pathology, medical/surgical oncology, and scientific innovation. The studies encompassed by this career development award will be critical to obtain the training, knowledge, and expertise needed to successfully establish an independent translational sarcoma research program and apply for a tenure-track physician-scientist position in academic pathology. The proposed research will be performed under the mentorship of Dr. Jonathan A. Fletcher, leader of two international GIST research consortia, with guidance from an interdisciplinary Scientific Advisory Committee composed of leading experts in the sarcoma field. Environment: Brigham and Women?s Hospital (BWH) houses internationally recognized research programs in scientific discovery training physician-scientists for leadership roles in translational research. The BWH Department of Pathology is home to global leaders in sarcoma/GIST diagnostics, biology, and genetics, who collaborate effectively with clinical disciplines to leverage scientific discoveries into clinical practice for improved diagnosis and treatment.